diff --git a/src/target-sc/ilator.cc b/src/target-sc/ilator.cc
index 4f76ffc93..cb6d95965 100644
--- a/src/target-sc/ilator.cc
+++ b/src/target-sc/ilator.cc
@@ -574,9 +574,17 @@ bool Ilator::GenerateGlobalHeader(const std::string& dir) {
                  "#include <systemc.h>\n"
 #ifdef ILATOR_PRECISE_MEM
                  "#include <map>\n"
+                 "#include <unordered_map>\n"
 #else
                  "#include <unordered_map>\n"
 #endif
+                 // add a customized hash function for unordered map
+                 "struct MemAddrHashFunc {{\n"
+                 "  std::size_t operator() (int const& addr) const noexcept {{\n"
+                 "    return addr;\n"
+                 "  }}\n"
+                 "}};\n"
+
                  "SC_MODULE({project}) {{\n"
                 //  "  extern int instr_cntr;\n"
                  "  std::ofstream instr_log;\n"
@@ -840,7 +848,11 @@ std::string Ilator::GetCxxType(const SortPtr& sort) {
     ILA_ASSERT(sort->is_mem());
 #ifdef ILATOR_PRECISE_MEM
     return fmt::format(
-        "std::map<sc_biguint<{addr_width}>, sc_biguint<{data_width}>>",
+        // "std::map<sc_biguint<{addr_width}>, sc_biguint<{data_width}>>",
+        // try to switch to unordered_map for memory type to improve access speed.
+        // sc_biguint seems unhashable
+        // "std::unordered_map<sc_biguint<{addr_width}>, sc_biguint<{data_width}>>",
+        "std::unordered_map<int, sc_biguint<{data_width}>, MemAddrHashFunc>",
         fmt::arg("addr_width", sort->addr_width()),
         fmt::arg("data_width", sort->data_width()));
 #else
diff --git a/src/target-sc/ilator_dfs.cc b/src/target-sc/ilator_dfs.cc
index 34d8466a6..7624db274 100644
--- a/src/target-sc/ilator_dfs.cc
+++ b/src/target-sc/ilator_dfs.cc
@@ -102,7 +102,7 @@ void Ilator::DfsOpMemory(const ExprPtr& expr, StrBuff& buff, ExprVarMap& lut) {
   if (auto uid = asthub::GetUidExprOp(expr); uid == AstUidExprOp::kStore) {
     static const char* kMemStoreTemplate =
 #ifdef ILATOR_PRECISE_MEM
-        "tmp_memory[{address}] = {data};\n";
+        "tmp_memory[{address}.to_int()] = {data};\n";
 #else
         "tmp_memory[{address}.to_int()] = {data}.to_int();\n";
 #endif
@@ -156,7 +156,8 @@ void Ilator::DfsOpSpecial(const ExprPtr& expr, StrBuff& buff, ExprVarMap& lut) {
                    fmt::arg("memory_source", LookUp(expr->arg(0), lut)),
                    fmt::arg("address", LookUp(expr->arg(1), lut)),
 #ifdef ILATOR_PRECISE_MEM
-                   fmt::arg("mem_suffix", "")
+                  //  fmt::arg("mem_suffix", "")
+                  fmt::arg("mem_suffix", ".to_int()")
 #else
                    fmt::arg("mem_suffix", ".to_int()")
 #endif